Heating and cooling of buildings, like the production of hot water, are energy-demanding processes, and there are both economic and environmental grounds for reducing the quantity of energy that is utilized for these purposes. The requirement of a building or installation for heating/cooling naturally differs very considerably depending on its design, its use and its location. A residential building in Sweden, for example, normally has a heat requirement during the period between September and April, while a certain cooling requirement may exist during the period between May and August. A well-insulated office in Sweden with a large number of workers and many items of office equipment may instead have a cooling requirement in the daytime during a large part of the year. A building in a more southerly country may have a cooling requirement in the daytime, but a heating requirement at night, and so on.
Over recent decades, a large number of technical products have been produced and developed in order to improve the efficiency of these heating and cooling processes. Heat pumps are one product that has become increasingly common for heating applications in recent years. A heat pump normally comprises a system with an evaporator, a compressor, a condenser and a throttle valve, inside which system a cooling medium is caused to circulate. By evaporating the cooling medium at a lower pressure and condensing it at a higher pressure, thermal energy can be taken up at a lower energy (evaporation heat) and given off at a higher temperature (condensation heat). Heat pumps are able to take up heat, for example from lakes, bore holes (“rock heat”), outdoor air and extract air (that is to say air that is discharged from a building by ventilation), and to give off heat to the indoor air, for example, or for water heating. Heat pumps have also been used for quite a long time for the cooling of buildings in the form of air conditioning installations, in which heat is taken from a building and is discharged to the outside. A heat pump requires electricity in order to drive the compressor, and the price of electricity is accordingly an important parameter for the economic viability of a heat pump. In colder climates, the effect of a heat pump is not normally sufficient to cope with heating unassisted, for which reason buildings are equipped with supplementary heating systems.
In order further to improve the efficiency of heating systems, it is customary to attempt to utilize solar radiation. One example is to cause water to circulate in a solar-heated system in order, by so doing, to obtain a “free” contribution to the production of hot water. Another example is provided in U.S. Pat. No. 4,378,787, according to which an outdoor air heat pump is positioned in a loft space provided with a window, which permits heating of the outdoor air by solar irradiation.
In recent years, development work has been targeted to a great extent at heat pump components and cooling media, among other things with a view to maintaining the efficiency of outdoor air heat pumps at increasingly low outdoor temperatures.